The present invention relates to a process and system to optimize optical inter-satellite links.
Optical free-space communication between satellites and between a satellite and the ground station will gain importance in the near future because it represents, among other factors, a weight-saving alternative to the existing microwave technology onboard the satellites.
So-called optical terminals consist of one or several telescopes that restrict the angular range of the visual field of an optical receiver in the direction of an opposite station and also guarantee the directional emission of the signals to be sent. A number of movable optical elements are furthermore provided to align the direction of transmission and reception.
Besides the direct detection of the optical output of the opposite station as the method of transmission, an important role also falls to the coherent heterodyning of the received light with the light of the same frequency from a local oscillator laser. This is because both a high sensitivity to the signal to be detected and an insensitivity to interferences by radiation present in the background are important.
The major advantage of using light instead of high-frequency waves as the transmission medium is the resulting higher system efficiency based on the shorter wavelength (by a factor of 10,000) and the consequent higher antenna gain.
The main difficulty, however, results from the fact that the smaller beam divergence requires a high alignment accuracy of the transmitter and receiver telescopes with great precision and long-term stability of the mechanisms of the optical communication terminal. The sometimes-high relative speeds of the satellites furthermore require that a point-ahead between the alignment of the receiver and transmitter telescopes be calculated and precisely adjusted.
These demands for precision result in highly complex and expensive mechanisms which, to ensure their long-term stability, must be readjusted at regular intervals with the aid of special apparatus. Furthermore, a high safety margin is required for the transmitter output. The resulting high system complexity, high cost, and high energy consumption often make the use of light unattractive in comparison with the high-frequency technology.
It is therefore the object of the present invention to prevent the above shortcomings of the prior art.
This object is accomplished according to the invention with a process which allows the terminals to transmit operation-internal data that need not necessarily be visible to the operator of the terminal, making it possible to carry out adjustments and compensate for age-related changes in addition to performing the terminal-internal network management.
The process of the invention has the advantage that it permits, in an exceptional manner, the use of an auxiliary channel to continually monitor and optimize: the calibration and adjustment of the opto-mechanical components; the frequency accuracy and adjustment ranges of the oscillators; and the level of transmission power of an optical transmission terminal while it is in operation. This considerably reduces the requirements for manufacturing accuracy and slow aging over the course of the useful life, and also makes it possible to reduce the terminal""s power consumption.
It furthermore overcomes the shortcoming of the prior art that the satellite operator can measure and subsequently readjust the actual orbits of his satellites only via orbit measurements performed from ground stations.
With the process of the invention, in contrast, the demands on the accuracy of the orbit and position measurement on one hand may be lower, and the actual orbit/position data on the other hand can be calculated and subsequently implemented much more precisely if the exact distance between the satellites and their exact alignment are first calculated with the process of the invention.
Further details, features and advantages of the invention result not only from the claims and characteristics described thereinxe2x80x94by themselves and/or in combination with each otherxe2x80x94but also from the following description of a sample embodiment.